Oncornavirus of guinea pigs. 1. Morphology and distribution in normal and leukemic guinea pig cells.

Two morphologically distinct types of oncornavirus particles were observed in guinea pig cells. In tissues of leukemic guinea pigs, intracisternal A-type particles 90–100-nm diameter, predominated. Extracellular particles with dense core, approximately 90–110 nm in diameter, were seen only occasionally at the intercellular space of the tissues, but were predominant in plasma and sera of the same animals. Placental and fetal tissues obtained from normal guinea pigs showed only intracisternal A-type particles. Cultured guinea pig cells when treated with BrdU revealed many intracytoplasmic A-type particles 90–100-nm diameter. Budding of these A-type particles at the cell membrane to form extracellular enveloped A-type particles was observed. Extracellular virus particles with dense cores, 110–120 nm in diameter, similar to those seen in tissues and plasma of leukemic guinea pigs, were abundant in the BrdU-treated cultures. The morphology and distribution of the intracellular and extracellular virus particles in tissues and tissue cultures derived from leukemic and normal guinea pigs are compared, and the relationships between these virus particles are discussed.     

Histopathologic and ultrastructural studies of disseminated cytomegalovirus infection in strain 2 guinea pigs

Inbred strain 2 guinea pigs developed severe disseminated disease during acute experimental guinea pig cytomegalovirus (GPCMV) infection. A high mortality rate (100%) resulted, with most animals dying between 10 and 14 days after high dose (7.5 X 10(5) TCID50) virus inoculation. Infectious virus was recovered from many tissues, including spleen, lungs, liver, pancreas, heart, adrenals, kidneys, and salivary glands. The rate of GPCMV isolation from these tissues ranged from 50 to 100%. Gross lesions were observed in the spleen, liver, and lungs. On histologic examination, lesions were also seen in many other organs, including heart, pancreas, kidneys, adrenals, brain, intestines, and salivary glands. Intranuclear viral inclusions were present in many cell types of various organs. Under electron microscopic examination, cells with viral inclusions were easily found in the spleen, and liver, but less readily in the lungs, kidneys, salivary glands, and other organs. Most of the intranuclear inclusions consisted of electron-dense fibrils (10 nm diameter), viral nucleocapsids (100 nm), and tubular structures (60 nm diameter). Dense bodies and enveloped dense virions containing single or multiple capsids were present in the cytoplasm of many infected cells. The morphologic developments of GPCMV in these visceral tissues of strain 2 guinea pigs resembled those seen in GPCMV-infected cultured guinea pig cells but differed from those observed in the infected salivary gland duct cells. Strain 2 guinea pigs are a useful animal model for studying disseminated infection in CMV-associated human diseases.     

Ultrastructural studies of the envelopment and release of guinea pig herpes-like virus in cultured cells

The process of envelopment and release of guinea pig herpes-like virus was examined in both infected guinea pig kidney and thymus tissue culture cells by electron microscopy. The majority of the nucleocapsids were enveloped by budding into nuclear vacuoles; some were enveloped by budding from the inner nuclear membrane. Budding into cytoplasmic vacuoles was also seen. Many enveloped virus particles inside the nuclear vacuoles were pear shaped with a tail-like structure. Approximately 23% of pear-shaped virus particles were seen in the infected thymus fibroblastic cells, but only 6% were found in the infected epithelial cells. The envelopes of all nuclear enveloped virus particles appeared as smooth membranes, while the majority of particles exhibiting fuzzy and thick dense envelopes were seen in the cytoplasm or extracellular space. The average diameter of the cytoplasmic or extracellular enveloped virus particles was approximately 167 nm, and the average diameter of the nuclear enveloped virus particles was about 146 nm.Data also showed that mature nuclear virus particles were first released into perinuclear cisterna and then traveled through cytoplasmic channels to the extracellular space.     

Comparison of guinea pig cytomegalovirus and guinea pig herpes-like virus: growth characteristics and antigentic relationship.

The growth characteristics of guinea pig cytomegalovirus (GPCMV) and guinea pig herpes-like virus (GPHLV) in cell cultures were compared. Guinea pig fibroblast cells were highly susceptible to infection with both viruses, whereas guinea pig kidney cells were sensitive only to GPHLV. No cytopathic effect was observed in the latter cell system after infection with GPCMV,nor was there an increase in virus titer, although the cirus persisted in the kidney cells for 2 to 3 weeks postinfection. Electron microscope studies showed nonvirion tubular structures in GPCMV -infected fibroblast cells, but not in GPHLV- infected cells. Large packages of enveloped nuclear virus particles were commonly seen in GPHLV -infected cells, especially kidney epithelial cells, but none were found in the GPCMV -infected fibroblasts. Complete enveloped extracellular virus particles were present in both virus-cell systems. Both viruses showed narrow host spectra and replicated well only in guinea pig cells although GPHLV multiplied to some degree in rabbit cells. No antigenic relationship could be demonstrated between the two viruses using antisera specific for each virus that was produced in rabbits and guinea pigs. Rabbits produced high neutralizing antibody titers to GPHLV, whereas guinea pigs were the animals of choice for GPCMV antiserum production.     

Comparison of guinea pig cytomegalovirus and guinea pig herpes-like virus: pathogenesis and persistence in experimentally infected animals.

The pathogenesis of guinea pig cytomegalovirus (GPCMV) and guinea pig herpes-like virus (GPHLV) in guinea pigs was compared. Animals were inoculated with the two viruses by different routes and sacrificed after varying periods of time. GPCMV was consistently isolated from salivary gland 2 weeks postinoculation and thereafter following intraperitoneal or subcutaneous incoulaton. Virus was less frequently found in other tissues including blood, spleen, and kidney. Intranuclear inclusions were seen in tissue sections of salivary gland after inoculation with GPCMV- infected tissue suspension, but were only rarely found after inoculation with tissue culture virus. In GPHLV-infected guinea pigs, consistent latent infection of leukocytes and other tissues was detected by cocultivation techniques. Intranuclear inclusions were not found in the spleen, salivary gland, or other infected tissues after GPHLV infection with either tissue culture virus or infected tissue suspension. Guinea pigs inoculated with GPCMV produced high titers of specific neutralizing antibody to the homologous virus; those inoculated with GPHLV developed long-term viremia accompanied by minimal neutralizing antibody levels to the virus.     

A guinea pig model for Lyme disease.

We report that outbred Hartley guinea pigs are susceptible to Borrelia burgdorferi. We recovered spirochetes from 57 of 60 (95%) guinea pigs inoculated when < or = 3 months of age. In contrast, animals inoculated when > or = 6 months of age were resistant to infection as defined by recovery of organisms at > or = 4 weeks postinoculation. Infection was widely disseminated: B. burgdorferi was recovered from 83% of bladders, 64% of knee joints, 57% of hearts, 48% of spleens, and 38% of spinal cords examined within 4 weeks of inoculation. Histopathologic changes were common in the heart (88%) (preferential involvement of perineural tissues near the annulus fibrosus) and bladder (76%) and were also noted in a minority of spinal cords (13%) and knee joints (9%). Western immunoblots demonstrated an immunoglobulin G response to B. burgdorferi, particularly to the 24-, 31- (OspA), 39-, and 41-kDa (flagellin) antigens. Infection was cleared from most tissues with the passage of time; spirochetes were recovered from 63% of tissues removed from guinea pigs at < or = 4 weeks after inoculation but from only 32% at > or = 8 weeks postinoculation (P < 0.001). An exception was the failure to clear spirochetes from infected knees, 90% of which were culture positive even when evaluated at > or = 8 weeks postinoculation. The guinea pig provides a new model useful for studying host-spirochete interactions in Lyme disease.     

A latent guinea pig herpes-like virus: isolation and envelopment.

A guinea pig herpes-like virus (GPHLV) has been isolated from randomly selected guinea pigs. This virus is serologically related, if not identical, to the guinea pig herpes-like virus isolated by Hsiung-Kaplow. The frequency of latent infection in guinea pigs was found to be highly variable among animals of the same commercial origin. Ultrastructural studies have shown that the morphological development of this virus was similar to that reported for other herpes viruses in the early stages, but frequently differed at the envelopment stage. In the cytoplasm, virus particles were associated with electron-dense zones from which they acquired a thick and rough envelope.     

Centrifugal elutriation studies in mast cells from rats,guinea pigs and man

Elutriation is a cell separation method based on countercurrent centrifugation. For mast cell purificaiton it is superior to density gradient methods since no foreign protein or dense material has to be removed from the purified cells. The elutriation profiles of peritoneal rat mast cells differ considerably if the cells come from non-sensitized or actively sensitized donor animals and/or from different strains. This result is another indication of an altered morphological state of mast cells due to active immunization and is dependent on genetic factors.Cell aggregation proved to be the main obstacle to elutriation purification of guinea pig tissue mast cells. Human mast cells from adenoid tissues, however, could be brought to 70–90% purity, even if the elutriation profiles varied from donor to donor.     

Porcine cytomegalic inclusion disease virus

Summary An electron microscopic study was made on porcine cytomegalic inclusion disease virus in the nasal mucosa of three piglets from a herd with a history of generalized cytomegalic inclusion disease. In addition to previously described viral developmental forms within the nucleus and enveloped virus particles between the nuclear membranes, the study revealed enveloped virus particles within membrane-enclosed clusters in the nucleus, and reduplication of nuclear membranes. In the cytoplasm, enveloped virus particles, 120–150 m in diameter, were found within vacuoles. Unenveloped virus particles, 90–110 m in diameter, were located free in the cytoplasm and often showed a crystal pattern.In the nucleus, the crystal pattern of virus particles could not be detected. In the cytoplasm, various viral forms were also found within a dense osmiophilic matrix which is regarded as the site of virus destruction.The mode of acquiring viral envelopes within the nucleus is discussed.     

The blood indices of the healthy guinea pig

Summary Statistical results on the blood indices of healthy guinea pigs are given. For the first time a distribution curve has been obtained which shows the stability of healthy guinea pig erythrocytes to lysis in acid solution; the measurements were made by the method of Gitel'zon and Terskov.(Presented by Academician V. N. Chernigovskii) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 52, No. 7, pp. 115–118, July, 1961     

Cytomegalovirus-induced mononucleosis in guinea pigs.

The effects of cytomegalovirus (CMV) infection on hematopoietic and lymphoid tissues were studied in guinea pigs. Blood parameters, histopathology, and virus distribution in the bone marrow, spleen, lymph nodes, and thymus were assessed during primary nonlethal acute and chronic guinea pig CMV infection. Transient hematological changes comparable to those seen in human CMV mononucleosis were observed during acute infection. These included anemia and leukocytosis with atypical lymphocytes. Splenomegaly and stimulation of spleen and lymph node T- and B-cell areas were also noted. These changes occurred at the peak of virus recovery from all tissues tested, as well as from macrophages and B- and T- cell-enriched spleen subpopulations. Virus was cleared rapidly from blood and bone marrow; blood counts, spleen size, and histology returned to normal within 1 month after virus inoculation. However, guinea pigs failed to eliminate the virus completely from lymphoid tissues, since virus persisted in splenic macrophage and B-lymphocyte-enriched populations during chronic infection. The data suggest that CMV-infected mononuclear cells play a role in the establishment of generalized acute infection and virus persistence.     

Congenital and perinatal infection with Junin virus in guinea pigs

Junin virus infection in guinea pigs is known to be similar to human Argentine hemorrhagic fever (AHF). The guinea pig was chosen as a model for transplacental transmission of Junin virus, as both guinea pig and man have a similar placental structure. Pregnant guinea pigs were infected with the pathogenic XJ strain of Junin virus intramuscularly route at different stages of pregnancy. The group infected during the last third of pregnancy produced 16 newborn, but mortality reached 100%: 18% were born with typical AHF hemorrhagic signs, 54% without signs, and the remainder were stillborn. Virus was recovered from organs of newborns, as well as placental tissues. A second group, infected in the second third of pregnancy, died with intrauterine fetuses, all of which showed hemorrhagic signs and virus present. In a last group, infected in the first third of pregnancy, fetuses were free from macroscopic lesions. In order to determine whether lactation may be an alternative infection route in guinea pigs, mother guinea pigs were infected with Junin virus at different times postparturition. The 84% noninfected newborn housed together with their infected mothers died during the suckling period, half with typical AHF signs. Junin virus transmission from mother to fetus was thus proved, and lactation may be considered as an alternative perinatal infection route.     

Antigen-induced late-phase airway obstruction in the guinea pig?

Hartley or Dunkin-Hartley guinea pigs (n=136) were actively sensitized to ovalbumin orAscaris suum protein by five different regimes. Specific airway resistance (sR _AW) was measured in conscious animals by a plethysmographic procedure before, immediately following and at various intervals (up to 96 h) after aerosolized antigen or vehicle challenge. Each sensitization and challenge regime produced an immediate allergic response with positive responses (defined as a 2-fold increase in sR _AW) in 78–100% of animals. Recovery from the immediate response followed by late-phase responses was observed in only two out of a group of four animals. The results failed to substantiate literature reports of a high incidence of late responses in the guinea pig at 4–8, 17–24 or 72 h after allergen challenge.     

Prostaglandins and neurotransmission at the guinea pig and rabbit urinary bladder

High concentrations of prostaglandins (PGE₁, PGE₂, or PGE₂) (2×10^–6 M) produced a slow contraction of longitudinal strips of detrusor muscle taken from the bladders of guinea pigs and rabbits. At a lower concentration (10^–6 M) prostaglandins enhanced contractions produced by field stimulation of nerves in guinea pig but not rabbit strips. The contractions were not affected by indomethacin. Contractions of guinea pig strips in response to acetylcholine at 10^–4 M were enhanced by prostaglandins and unaffected by indomethacin. Membrane potentials of smooth muscle cells recorded with micro electrodes, were unchanged up to 10^–6 M PGE₂. Above this the cells were depolarized with an increase in frequency of spontaneous action potentials. Synchronous recording of electrical and mechanical activity with the double sucrose gap indicated a decrease in amplitude of the evoked excitatory junction potential and action potential even when the contraction was enhanced in the presence of PGE₂. Responses to repeated stimulation at 10 Hz for 1 min were progressively depressed. This trend was slightly reduced by PGE₂ but unaffected by indomethacin. It is concluded that prostaglandins are not normally released by the nerves to the urinary bladder but are able to facilitate contraction in the guinea pig. This effect is probably on the excitatory-contraction coupling, possibly by mobilizing Ca²⁺. Some modification of transmitter release by the nerves may also occur.     

Experimental infection and immune response of guinea pigs with varicella-zoster virus.

An immune response (fluorescent antibody to membrane antigen) was detected in guinea pigs inoculated with varicella-zoster virus (VZV) adapted to guinea pig embryonic cells, including the Oka vaccine strain, even when inoculation was by an external route, i.e., nasal or corneal. Live or UV-inactivated virus having the same virus titer before irradiation was administered to guinea pigs by the corneal route, and antibody induction was detected only with live virus. The transmission of VZV from infected guinea pigs to noninfected ones was suggested by the appearance of antibody in the serum of the latter, who were kept in the same cage. The time course of the appearance of humoral and cellular immune responses in guinea pigs was examined by the fluorescent antibody to membrane antigen test and the skin reaction, with varicella antigen representing delayed-type hypersensitivity. When VZV was injected subcutaneously, skin reaction appeared as early as 4 days after inoculation, which preceded the appearance of detectable antibody by 2 to 6 days. In in vitro studies, the Oka vaccine showed a higher adsorption rate and better growth in guinea pig embryonic cells than did other wild-type strains when assayed by the infectious center assay. These results suggest that a system of VZV adapted to guinea pig cells and guinea pigs provides a good animal experimental model for immunological study of VZV infection.     

Non-infectious intracisternal A-type particles in a sarcoma-positive,leukemia-negative mouse cell line transformed by murine sarcoma virus (MSV)

Summary Cell lines derived from C3H mouse embryos are described. Untransformed MO-cells were found susceptible to transformation by Kirsten MSV. Two types of transformed cell lines were isolated. MO-P-cells produced infectious MSV and contained extracellular C-type particles. MO4-cells did not release infectious focus forming virus; however, upon superinfection with murine leukemia viruses (MLV), infectious MSV was released. Not superinfected MO4-cells contained multiple intracisternal A-type particles. In this respect these cells differ from the MSV genome-carrying NP-cells (1) which do not produce particles nor viral antigen, and from S⁺L^–-cells (2) which release extracellular, non-infectious C-type particles.     

Morphologic characteristics and nucleic acid type of transmissible gastroenteritis virus of pigs

Summary The morphology and development of transmissible gastroenteritis (TGE) virus of pigs have been studied with the electron microscope. By the negative contrast technique characteristic particles were found in preparations concentrated and partially purified either from infected fetal pig kidney cell cultures by phase partition in dextran-methylcellulose and dextran-polyethylene glycol followed by equilibrium zonal centrifugation or from infected fetal pig thyroid (FPT) cell cultures by differential centrifugation. Most of the particles had a spherical shape and were between 75 and 120 m in diameter. In some particles disrupted spontaneously, fixed with formaldehyde or split with ether, an outer membrane and internal beaded filaments were demonstrated.In thin sections of cultured FPT cells infected with the virus, a small number of intracytoplasmic virus particles could be detected 4 hours after infection. The particles increased in number, both intra- and extracellularly, with the lapse of time, concomitant with the increase in amount of infective virus in cultures. The virus particle consisted of a dense nucleoid 40–60 m in diameter separated by a zone of lesser density from a limiting membrane 56–81 m in diameter. On the basis of morphological observations, it was suggested that the virus particle matures at the inner surface of the membrane which lines the cisternae of endoplasmic reticulum, perinuclear cisterna, and cytoplasmic vacuoles of unknown origin. Multiplication of TGE virus was not inhibited by 5-iododeoxyuridine suggesting that its nucleic acid is RNA. Similarity between TGE virus and some of the myxoviruses, as well as some oncogenic viruses was discussed.This investigation was supported in part by funds provided by the Research Committee of the Graduate School and Fromm Laboratories, Grafton, Wisconsin.Published with the approval of the Director of the Wisconsin Agricultural Experiment Station as paper N.S. 532.The authors gratefully acknowledge the opportunity for the use of the electron microscope provided by Dr.Carl Olson.     

Ultrastructural development of guinea pig cytomegalovirus in cultured guinea pig embryo cells.

The ultrastructural development of guinea pig cytomegalovirus (GPCMV) in guinea pig embryo cells was studied using electron microscopy. Tubular structures were found in nuclei of virus infected cells, followed by the appearance of intranuclear inclusions containing virus nucleocapsids. While some nucleocapsids were enveloped at the inner nuclear membrane, others were released into the cytoplasm where they were associated with, or within, dense matrix which was subsequently enveloped by cytoplasmic membranes to form enveloped dense virions. Dense bodies without virus capsids were formed in the cytoplasm and enveloped in a similar manner. An involvement of the nuclear pores in the release of unenveloped virus capsids from the nucleus to the cytoplasm was postulated. Evidence that the enveloped dense virions and dense bodies shared common envelope antigen(s) was obtained by immunoelectron microscopy. The similarities and differences in the ultrastructural development of GPCMV and other cytomegaloviruses are discussed.     

Rotavirus-Like, Calicivirus-Like, and 23-nm Virus-Like Particles Associated with Diarrhea in Young Pigs

Virus particles morphologically similar to caliciviruses and rotaviruses were detected by electron microscopy (EM) in the intestinal contents of a 27-day-old diarrheic nursing pig. A third small spherical 23-nm virus-like particle was also observed. Calicivirus-like particles averaged 33 nm in diameter. Similar to rotaviruses, rotavirus-like particles were present as single-capsid 55-nm forms or double-capsid 70-nm particles. Most gnotobiotic pigs orally exposed to samples containing these three viruses developed diarrhea and villous atrophy of the small intestine, and all shed the three viruses in their intestinal contents. Attempts to propagate these viruses in cell culture were unsuccessful. The antigenic relationship of the rotavirus-like particles to known rotaviruses was explored by immune EM and immunofluorescent staining. By these techniques, the rotavirus-like particles did not cross-react with antisera to porcine, bovine, or human rotaviruses or to reovirus type 3. Antisera from gnotobiotic pigs exposed to all three viruses had enzyme-linked immunosorbent assay and virus neutralization titers of <4 against porcine rotavirus. Previous infection of gnotobiotic pigs with the mixture containing rotavirus-like particles failed to protect them against a subsequent challenge with porcine rotavirus. The antigenic relationship of the calicivirus-like particles to known caliciviruses was investigated by immune EM and virus neutralization. By these tests, the calicivirus-like particles did not react with antisera against feline calicivirus strain 255 or M-8. In a study conducted at Plum Island Animal Disease Center, antiserum against the three combined agents did not specifically neutralize any serotype of swine vesicular exanthema virus.     

Reactions of lymphocytes and macrophages of guinea pigs to toxic action of influenza virus

Influenza ciruses differing in their virulence to man have different effects on lymphocytes and macrophages in the peritoneal exudate of intraperitoneally infected guinea pigs. With strengthening of the virulent properties of influenza viruses for man, their inhibitory action on guinea pig lymphocytes and macrophages also intensifies. Weakly virulent strains of influenza viruses cause a substantial increase in the functional activity of macrophages but they have no lympholytic properties. Since differences in the cell composition of the exudate and in the functional state of the macrophages correlated with the degree of virulence of the viruses to man, the study of responses of lymphocytes and macrophages of animals resistant to influenza virus can be used to determine the toxic properties of test viruses.Laboratory of Pathogenesis and Pathomorphology and Laboratory of the Etiology of Influenza and Acute Respiratory Diseases, All-Union Research Institute of Influenza, Ministry of Health of the USSR, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the USSR, A. A. Smorodintsev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 4, pp. 497–499, April, 1976.